Pine Pienaar wrote:
Can I ask that "someone" run these numbers for me
and let me have it so I
figure out what I doing wrong.
I use the following input data
BHP 180 RPM 2700 Sea level speed 240
That is a very clean airplane. What kind of airplane
are we talking about
here.
I'm using 5.63" at station 1 (Ave 4.4")
Airplane frontal surface 1.05 ft^2 Cd 0.2 (I
think)
Design altitude 8000 ft
I would like to use the Clark-Y blade profile as I
think it would be more
robust and take possible stone damage better than
the proposed NACA 16106
Pine Pienaar
pine@cpro.co.za
Lancair 360 #664
Vance Jaqua wrote:
Vance here - With a rigid fixed pitch prop and this
speed range you have a real problem. My prop size
program suggests for a 70 inch diameter prop a ptch of
about 97 t0 98 inches with blade widths at .9 R 3.25
in at .7R 4 inch at .5R 5 inch and .3R 6 inch. The
program adjusts blade widths for a uniform hp per sq
ft over the working range of the disk (.2 on out)
generally tip further narrowing is suggested in the
last 10 percent to reduce tip losses.
Using a typical
180 bhp aircraft engine power curve, you are, of
course, grossly stalled and bogged down at static to
about 1900 rpm where the hp is about 108, and thust is
about 306 lbs.
It gets even worse on the roll as
sections start unstalling and bog the engine down even
further at 60 mph 1800 rpm about 97 bhp and 304 lbs. At
100 it is not much better 1900 again and about 280
lbs. Even at 140 a little over 2100 rpm 130 hp 275
lbs, 180 just under 2400 160 hp 280 lbs, 220 a tad
over 2600 almost 180 hp 265 lbs, and at 240 slightly
over speed about 2750 190 hp 260 lbs.
The take off
roll would be long and the climb suffers. The good
news is that with more flexible props of proper blade
shape, like Klaus and others provide, the low end rpm
and power come up, and performance is improved. In
terms of airfoil, props do not benefit as much as
wings from fancy foils because of the low Reynolds
numbers. Vance
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